Abstract

Most instruments for measuring radon concentrations in the air should be calibrated using air with known radon concentrations, obtained from a solution of radium. However, safe handling of such a solution of alpha‐active elements can be troublesome. Standard gamma‐ray sources of low activity are handled more safely and typically used to obtain the absolute detection efficiency of a Ge detector with high accuracy. A new method has been developed to calibrate a radon detector with such sources. A radon exhalation rate for a substance containing a small amount of radium is measured with the radon detector to be calibrated. After this, the vessel containing the radium is sealed so that the radon does not escape from it. The buildup of the activity of 214Bi in it is obtained from gamma‐ray measurements and gives the radon exhalation rate on the basis of the activity of the standard sources. From the comparison between the two values of the exhalation rate, the radon detector is calibrated. A plane multiwire‐electrode ionization chamber is used as a radon detector, and its detection efficiency is calculated from its geometrical form. The radon exhalation rate computed from the calculated efficiency agrees with that determined from the activity of the standard gamma‐ray sources within their specified 6% error.